Objective lens

Abstract

The objective lens provided by the invention has the advantages of long working distance, high numerical aperture and good aberration performance. An objective lens 1 includes, in order from the object side: a first lens group having a positive refractive power and including three or more lens components; a second lens group which has the highest light height and moves on the optical axis; a third lens group including a lens component having a concave surface facing the image side at a position closest to the image side of the third lens group; and a fourth lens group including a lens component having a concave surface facing the object side at a position closest to the object side of the fourth lens group, the first lens group including a cemented lens at a position closer to the image side than the lens component closest to the object side of the first lens group.

Description

Technical Field

[0001] The disclosure in this specification relates to the objective lens. Background Technology

[0002] In recent years, research using cell aggregates such as spheroids and organoids, which collect large numbers of cells and culture them in three dimensions, has attracted attention. Such samples are, for example, about 100 μm to 500 μm in size, so liquid immersion system objectives are generally used for deep cell observation.

[0003] In immersion system objectives, a higher numerical aperture than that of dry system objectives is achieved by filling the space between the objective and the sample (more precisely, the sample holding component) with immersion liquid, thereby enabling observation at high resolution and with high brightness. Furthermore, by using an immersion liquid with a refractive index close to that of the sample, spherical aberration caused by refractive index mismatch at the sample-immersion interface can be suppressed. The deeper the observation position, the more significant the effect of spherical aberration caused by refractive index mismatch; therefore, by suppressing spherical aberration, deeper positions can be observed.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: US Patent No. 10,732,395 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] To observe the deep parts of the sample as described above, a longer working distance is required. Patent Document 1 describes an immersion system objective lens for a microscope with a long working distance. However, its numerical aperture is slightly smaller, and there is room for improvement in chromatic aberration performance. Therefore, an objective lens with a long working distance and a higher numerical aperture, exhibiting good aberration performance, is desired.

[0009] In view of the above-mentioned actual situation, one aspect of the object of the present invention is to provide an objective lens with a long working distance and good aberration performance, having a high numerical aperture.

[0010] Methods for solving problems

[0011] An objective lens of one embodiment of the present invention comprises, from the object side, the following components in sequence: a first lens group having positive refractive power and comprising three or more lens elements; a second lens group having the highest ray height and moving along the optical axis; a third lens group comprising a lens element with a concave surface facing the image side at the position closest to the image side of the third lens group; and a fourth lens group comprising a lens element with a concave surface facing the object side at the position closest to the object side of the fourth lens group, wherein the first lens group comprises a conjoint lens at a position closer to the image side than the lens element closest to the object side of the first lens group.

[0012] Invention Effects

[0013] Based on the above method, it is possible to provide objectives with long working distances, high numerical apertures, and good aberration performance. Attached Figure Description

[0014] Figure 1 This is a cross-sectional view of objective lens 1 in Embodiment 1 of the present invention.

[0015] Figure 2 This is a cross-sectional view of the imaging lens 10.

[0016] Figure 3 This is an aberration diagram of the optical system consisting of objective lens 1 and imaging lens 10 in its first state.

[0017] Figure 4 This is an aberration diagram of the second state of the optical system consisting of objective lens 1 and imaging lens 10.

[0018] Figure 5 This is a cross-sectional view of objective lens 2 in Embodiment 2 of the present invention.

[0019] Figure 6 This is an aberration diagram of the optical system consisting of objective lens 2 and imaging lens 10 in its first state.

[0020] Figure 7 This is an aberration diagram of the second state of the optical system consisting of objective lens 2 and imaging lens 10. Detailed Implementation

[0021] This application describes an objective lens according to one embodiment of the present application. The objective lens of this embodiment (hereinafter referred to as the objective lens) is an infinity-corrected microscope objective lens used in conjunction with an imaging lens. In this specification, a lens component, whether a single lens or a combined lens, refers to a lens block in which only the object-side surface and the image-side surface of the lens surface through which light from the object point passes are in contact with air. That is, one single lens is one lens component, and one combined lens is also one lens component. On the other hand, multiple single lenses or multiple combined lenses arranged through air are not referred to as one lens component. Furthermore, a concave-convex lens component refers to a lens component having a concave-convex lens shape, meaning that one of the object-side surface and the image-side surface of the lens component is concave and the other is convex.

[0022] The objective lens consists of a first lens group, a second lens group, a third lens group, and a fourth lens group, arranged sequentially from the object side, all possessing positive refractive power. The first lens group contains three or more lens components, and includes a conjoint lens positioned closer to the image side than the lens component closest to the object side. The second lens group is a movable group positioned at the highest point of the light beam and moving along the optical axis. In the third lens group, a lens component with its concave surface facing the image side is located closest to the image side. In the fourth lens group, a lens component with its concave surface facing the object side is located closest to the object side. That is, the third and fourth lens groups are configured with their concave surfaces facing each other.

[0023] In the objective lens configured as described above, the first lens group consists of three or more lens components, thereby allowing diverging light from the object point to converge gradually through the first lens group. Therefore, spherical aberration and coma can be suppressed to a minimum. Furthermore, the first lens group includes a conjoint lens in the region closer to the image side than the lens component closest to the object side, where both the off-axis principal ray and limb ray are higher. This conjoint lens can primarily correct on-axis chromatic aberration and magnification chromatic aberration.

[0024] Furthermore, in the aforementioned objective lens, by placing a second lens group after the first lens group, which has positive refractive power, light is incident on the second lens group in a state where the divergence of light from the object point is mitigated. Additionally, by configuring the second lens group, whose rim rays have the highest height, as a movable group that moves along the optical axis, the height of the rim rays passing through the second lens group can be significantly varied, thus sufficiently altering the amount of spherical aberration. Therefore, by moving the second lens group, spherical aberration caused by changes in observation depth, etc., can be effectively corrected.

[0025] Furthermore, in the objective lens, the third and fourth lens groups effectively correct various aberrations and convert the light passing through the second lens group into parallel light. Here, by setting the image-side surface of the third lens group and the object-side surface of the fourth lens group to be concave and facing each other (a so-called Gaussian group optical system), the height of peripheral rays in the opposing concave surfaces can be reduced. Therefore, Pezvalence can be effectively corrected, and image plane curvature can be significantly reduced.

[0026] The objective lens constructed as described above can achieve good aberration performance while maintaining a long working distance and high aberration range. The preferred structure of the objective lens will be described below.

[0027] Preferably, the first lens group comprises a combined lens consisting of a positive lens with a convex surface facing the image side and a concave-convex lens with a concave surface facing the object side at the position closest to the object. This structure can effectively correct for image plane curvature. More specifically, the concave surface of the concave-convex lens at the joint surface of the lens component closest to the object, which is incident before the luminous height increases at the edge, imparts a refractive effect, thereby effectively correcting for Pesvalle and Fibre.

[0028] The first lens group preferably comprises three joint lenses, and it is particularly preferred that the joint lens is disposed in a region closer to the image side than the lens component closest to the object side. In the image-side region of the first lens group, as described above, both the off-axis principal ray and the rim ray are elevated. Therefore, by arranging three joint lenses in this region, it is possible to primarily correct both on-axis chromatic aberration and magnification chromatic aberration.

[0029] Preferably, the second lens group consists of two joined lenses. By using two joined lenses in the second lens group where the edge rays are highest, chromatic aberration can be significantly corrected in addition to spherical aberration.

[0030] Preferably, the third lens group is composed of a single lens component. This avoids the increased manufacturing costs that would result from the third lens group being composed of multiple lens components.

[0031] The fourth lens group preferably comprises the image side of the lens element positioned closest to the object side, i.e., the lens element with its concave surface facing the object side, including both concave and convex lens elements with their concave surfaces facing the object side. This allows for better correction of chromatic aberration, astigmatism, and coma across a wide wavelength range. A more detailed explanation follows. In the fourth lens group positioned closest to the image side, to correct chromatic aberration, it is preferable to use lens pairs with different dispersion characteristics. However, if these are joined, the coma and astigmatism generated at the joining surface differ across wavelengths. Therefore, the fourth lens group is composed of the lens element that functions as the image side of the Gaussian group and one or more lens elements positioned across an air surface. This allows for the correction of patellar and astigmatism by providing one or more pairs of air interfaces, thus imparting differences in the refraction angles and ray heights of off-axis rays on these surfaces and effectively correcting astigmatism and coma. In particular, by including a concave-convex lens component with its concave surface facing the object side in one or more lens components, compared to plano-convex lenses and biconvex lenses, light can be refracted slowly before its height increases, thus particularly suppressing aberrations such as coma and astigmatism caused by off-axis properties. As a result, chromatic aberration, astigmatism, and coma can be corrected better over a wide wavelength range.

[0032] The objective lens is preferably configured to satisfy the following condition (1). Wherein, δ is the distance on the optical axis between the concave-object-side lens component and the concave-convex lens component of the fourth lens group. D is the distance on the optical axis from the specimen surface to the image-side lens surface of the fourth lens group (hereinafter also referred to as the total optical length). Furthermore, the specimen surface refers to the focal point where the infinity beam enters the objective lens from the image side, i.e., the surface including the front focal point.

[0033] 0.002≤δ / D≤0.02···(1)

[0034] Condition (1) mainly defines the air gap between the lens component positioned closest to the object in the fourth lens group and the concave-convex lens component with its concave surface facing the object. By satisfying condition (1), Pezvar correction can be effectively achieved. More specifically, by setting the air gap between the concave-object-facing lens component and the concave-convex lens component in the fourth lens group with δ / D as a lower limit or higher, interference between lenses can be avoided without setting the tolerances of each component too narrow. Furthermore, by narrowing the air gap between the concave-object-facing lens component and the concave-convex lens component in the fourth lens group with δ / D as an upper limit or lower, the concave-object-facing lens component constituting the Gaussian group can be made sufficiently thick while satisfying the predetermined total length of the objective lens. Therefore, Pezvar correction can be fully achieved.

[0035] Preferably, the fourth lens group has negative refractive power. By setting the fourth lens group to have negative refractive power, the rim light rays incident from the third lens group to the fourth lens group can be designed to be lower. Therefore, the relative concave surfaces of the third and fourth lens groups can effectively correct for Pezvar and significantly reduce image plane curvature.

[0036] Preferably, both the third and fourth lens groups include a joint lens. In the third lens group, the height of the rim rays increases. Therefore, by including a joint lens in the third lens group, on-axis chromatic aberration can be effectively corrected. Furthermore, in the fourth lens group, in addition to the height of the rim rays, the height of the off-axis principal rays also increases. Therefore, by including a joint lens in the fourth lens group, magnification chromatic aberration can be effectively corrected in addition to on-axis chromatic aberration. By configuring both lens groups to include a joint lens, both on-axis and off-axis chromatic aberration can be corrected more effectively.

[0037] The objective lens configured as described above is preferably moved via a second lens group to a position corresponding to an immersion liquid with a refractive index of 1.33 to 1.40, thereby enabling correction of spherical aberration. By using an immersion liquid with a refractive index ranging from 1.33 (equivalent to water) to 1.40 (equivalent to silicone oil), spherical aberration can be corrected, thus effectively correcting the amount of spherical aberration that may vary significantly due to differences in the refractive index of the immersion liquid.

[0038] Furthermore, the objective lens is preferably configured such that, by moving the second lens group to a position corresponding to the immersion liquid with a refractive index of 1.33 to 1.40, it can correct spherical aberration and satisfy the following conditions (2) and (3). Where f is the focal length of the objective lens. NA is the numerical aperture on the object side of the objective lens. WD is the working distance of the objective lens.

[0039] D / f≤7···(2)

[0040] D / (NA 2 •WD)≤35•··(3)

[0041] Condition (2) is a formula that specifies the relationship between focal length and total optical length. Condition (3) is a formula that specifies the relationship between total optical length, numerical aperture, and working distance. By making the objective lens satisfy condition (2), which substantially limits the total length, and also satisfy condition (3), it is possible to provide an objective lens that suppresses the total length of the objective lens within a specified range and has the necessary working distance and numerical aperture.

[0042] The following is a detailed description of embodiments of the above-mentioned objective lens.

[0043] (Example 1)

[0044] Figure 1This is a cross-sectional view of objective lens 1 in this embodiment. Objective lens 1 is an immersion system objective lens for a microscope. From the object side, objective lens 1 includes, in sequence, a first lens group G1, a second lens group G2, a third lens group G3, and a fourth lens group G4, all having positive refractive power. The space between the first lens group G1 and the glass cover C is filled with immersion liquid IM.

[0045] The first lens group G1, starting from the object side, includes, in sequence, a joint lens CL1, a lens L3 (a concave-convex lens with its concave surface facing the object side), and a joint lens CL2. The joint lens CL1 is formed by joining two lenses: lens L1 (a positive lens with its convex surface facing the image side) and lens L2 (a concave-convex lens with its concave surface facing the object side). The joint lens CL2 is formed by joining three lenses: lens L4 (a biconvex lens), lens L5 (a biconcave lens), and lens L6 (a biconvex lens).

[0046] The second lens group G2 consists of a joint lens CL3 that moves along the optical axis. The joint lens CL3 is formed by joining a biconvex lens L7 with a concave-convex lens L8 whose concave surface faces the object side.

[0047] The third lens group G3 includes the joint lens CL4. The joint lens CL4 is formed by joining two lenses together, namely the biconvex lens L9 and the biconcave lens L10.

[0048] The fourth lens group G4, starting from the object side, includes a joint lens CL5 and a lens L13 that is a concave-convex lens (concave-convex lens component) with its concave surface facing the object side. The joint lens CL5 is formed by joining two joint lenses: lens L11, which is a concave-convex lens with its concave surface facing the object side, and lens L12, which is a concave-convex lens with its concave surface facing the object side.

[0049] The data for objective lens 1 are as follows. Additionally, f1, f2 G1 f G2 f G3 f G4 n0 and ν0 are the focal lengths of objective lens 1, first lens group G1, second lens group G2, third lens group G3, and fourth lens group G4, respectively; the refractive index of the immersion liquid IM; and the Abbe number of the immersion liquid IM. The reference wavelength is the d-line. Furthermore, in this embodiment, silicone oil and water are used as the immersion liquid IM. Additionally, when silicone oil and water are used as the immersion liquid IM, f... G1 f G2 f G3 f G4 δ remains unchanged. On the other hand, fWD and D can vary depending on the immersion solution IM, and are therefore disclosed for each immersion solution IM.

[0050] f G1 =9.797mm, f G2=22.926mm, f G3 =-22.135mm, f G4 =-139.849mm, δ=0.504mm

[0051] (The immersion solution IM is silicone oil (n0 = 1.40410, ν0 = 51.90))

[0052] f=7.212mm, NA=0.85, WD=2.100mm, D=50.026mm

[0053] (The case where the immersion solution IM is water (n0 = 1.33304, ν0 = 55.79))

[0054] f=7.407mm, NA=0.85, WD=2.030mm, D=49.957mm

[0055] The lens data for objective lens 1 is as follows. Additionally, INF in the lens data represents infinity (∞).

[0056] Objective lens 1

[0057]

[0058]

[0059] Here, 's' represents the surface number, 'r' represents the radius of curvature (mm), 'd' represents the surface spacing (mm), 'nd' represents the refractive index, and 'νd' represents the Abbe number. The reference wavelength is the d-line (587.56 nm). These symbols remain the same in subsequent embodiments. Surfaces 's1' and 's2' represent the object-side surfaces of the glass cover CG, and surface 's3' represents the image-side surface of the glass cover CG. Surfaces 's4' and 's23' represent the object-side and image-side lens surfaces of the objective lens 1, respectively. For example, surface spacing 'd1' represents the distance on the optical axis from the surface 's1' to the surface 's2'. Surface spacing 'd23' represents the distance on the optical axis from the surface 's23' to the imaging lens; this distance is omitted in the lens data but is 110 mm.

[0060] When the state in which the second lens group is moved in relation to the silicone oil as the immersion liquid IM is designated as the first state, and the state in which the second lens group is moved in relation to the water as the immersion liquid IM is designated as the second state, the values ​​(in mm) of the intervals d12 and d15 in the lens data of each state, namely D1 and D2, and various parameters are as follows.

[0061]

[0062]

[0063] As shown below, objective lens 1 satisfies conditions (1) to (3) in both the first and second states.

[0064] (1) (First state) δ / D = 0.010

[0065] (1) (Second state) δ / D = 0.010

[0066] (2) (First state) D / f = 6.937

[0067] (2) (Second State) D / f = 6.745

[0068] (3)(First State)D / (NA) 2 ·WD)=32.972

[0069] (3)(Second State)D / (NA) 2 ·WD)=34.063

[0070] Figure 2 This is a cross-sectional view of the imaging lens 10 used in conjunction with the objective lens 1. The imaging lens 10 is a microscope imaging lens that forms a magnified image of an object when combined with an infinity-corrected objective lens. The imaging lens 10 consists of a conjoint lens CTL1 and a conjoint lens CTL2 arranged sequentially from the object side. The conjoint lens CTL1 is composed of two conjoint lenses: a lens TL1 that is a biconvex lens and a lens TL2 that is a concave-convex lens with its concave surface facing the object side. The conjoint lens CTL2 is composed of two conjoint lenses: a lens TL3 that is a biconvex lens and a lens TL4 that is a biconcave lens. The focal length ft of the imaging lens 10 is 180 mm.

[0071] The lens data for imaging lens 10 is as follows.

[0072] Imaging lens 10

[0073]

[0074] Figure 3 and Figure 4 This is an aberration diagram of an optical system consisting of objective lens 1 and imaging lens 10, showing the aberrations on the image plane formed by objective lens 1 and imaging lens 10 in the first state and the second state, respectively. Figure 3 of (a), Figure 4 (a) is a spherical aberration diagram. Figure 3 (b) Figure 4 (b) is a graph representing the quantity that violates the sinusoidal condition. Figure 3 (c) Figure 4 (c) is a scatter plot. Figure 3 (d) Figure 4(d) is the coma diagram at an image height ratio of 0.6 (image height 7.95 mm). Additionally, "M" in the diagram indicates meridional component, and "S" indicates sagittal component. Figure 3 and Figure 4 As shown, in this embodiment, aberrations are well corrected regardless of the immersion liquid.

[0075] (Example 2)

[0076] Figure 5 This is a cross-sectional view of objective lens 2 in this embodiment. Objective lens 2 is an immersion system objective lens for a microscope. From the object side, objective lens 2 sequentially includes a first lens group G1, a second lens group G2, a third lens group G3, and a fourth lens group G4, all having positive refractive power. The space between the first lens group G1 and the glass cover C is filled with immersion liquid IM.

[0077] The first lens group G1, starting from the object side, includes, in sequence, a joint lens CL1, a lens L3 (a concave-convex lens with its concave surface facing the object side), and a joint lens CL2. The joint lens CL1 is formed by joining two lenses: lens L1 (a positive lens with its convex surface facing the image side) and lens L2 (a concave-convex lens with its concave surface facing the object side). The joint lens CL2 is formed by joining three lenses: lens L4 (a biconvex lens), lens L5 (a biconcave lens), and lens L6 (a biconvex lens).

[0078] The second lens group G2 consists of a joint lens CL3 that moves along the optical axis. The joint lens CL3 is formed by joining a biconvex lens L7 with a concave-convex lens L8 whose concave surface faces the object side.

[0079] The third lens group G3 consists of a combined lens CL4. The combined lens CL4 is formed by joining two lenses: a biconvex lens L9 and a biconcave lens L10.

[0080] The fourth lens group G4, starting from the object side, includes a joint lens CL5 and a lens L13 that is a concave-convex lens (concave-convex lens component) with its concave surface facing the object side. The joint lens CL5 is formed by joining two joint lenses: lens L11, which is a concave-convex lens with its concave surface facing the object side, and lens L12, which is a concave-convex lens with its concave surface facing the object side.

[0081] The data for objective lens 2 are as follows.

[0082] f G1 =10.002mm, f G2 =23.436mm, f G3 =-21.584mm, f G4 =-139.219mm, δ=0.931mm

[0083] (The immersion solution IM is silicone oil (n0 = 1.40410, ν0 = 51.90))

[0084] f=7.214mm, NA=0.85, WD=2.100mm, D=50.074mm

[0085] (The case where the immersion solution IM is water (n0 = 1.33304, ν0 = 55.79))

[0086] f=7.399mm, NA=0.85, WD=2.032mm, D=50.007mm

[0087] The lens data for objective lens 2 is as follows.

[0088] Objective lens 2

[0089]

[0090] The values ​​of intervals d12 and d15 (in mm) in the lens data of the first and second states, namely D1 and D2, and various parameters are as follows.

[0091]

[0092]

[0093] As shown below, objective lens 2 satisfies conditions (1) to (3) in both the first and second states.

[0094] (1) (First state) δ / D = 0.019

[0095] (1) (Second state) δ / D = 0.019

[0096] (2) (First state) D / f = 6.942

[0097] (2) (Second state) D / f = 6.759

[0098] (3)(First State)D / (NA) 2 ·WD)=33.003

[0099] (3)(Second State)D / (NA) 2 ·WD)=34.059

[0100] Figure 6 and Figure 7 This is an aberration diagram of an optical system consisting of objective lens 2 and imaging lens 10, showing the aberrations on the image plane formed by objective lens 2 and imaging lens 10 in the first state and the second state, respectively. Figure 6 of (a), Figure 7 (a) is a spherical aberration diagram. Figure 6 (b) Figure 7 (b) is a graph representing the quantity that violates the sinusoidal condition. Figure 6 (c) Figure 7 (c) is a scatter plot. Figure 6 (d) Figure 7 (d) is the coma diagram at an image height ratio of 0.6 (image height 7.95 mm). Figure 6 and Figure 7 As shown, in this embodiment, aberrations are well corrected regardless of the immersion liquid.

[0101] Explanation of reference numerals in the attached figures

[0102] 1, 2: Objective lens, 10: Imaging lens, CG: Glass cover, CL1~CL5, CTL1, CTL2: Joint lens, G1: First lens group, G2: Second lens group, G3: Third lens group, G4: Fourth lens group, L1~L13, TL1~TL4: Lens.

Claims

1. An objective lens, characterized in that, The objective lens, starting from the object side, includes the following components: The first lens group has positive refractive power and contains more than three lens components; The second lens group has the highest light altitude and moves along the optical axis; The third lens group, at its position closest to the image side, includes a lens component with a concave surface facing the image side; and The fourth lens group includes a lens component with its concave surface facing the object side at the position closest to the object side. The first lens group includes a conjoint lens located on the image side, which is closer to the object side than the lens component of the first lens group that is closest to the object side.

2. The objective lens according to claim 1, characterized in that, The lens component of the first lens group closest to the object side is a combined lens consisting of a positive lens with a convex surface facing the image side and a concave-convex lens with a concave surface facing the object side.

3. The objective lens according to claim 1 or 2, characterized in that, The fourth lens group also includes a concave-convex lens component with its concave surface facing the object side on the image side of the lens component included in the fourth lens group.

4. The objective lens according to claim 3, characterized in that, The following conditional expressions are satisfied. 0.002≤δ / D≤0.02···(1) Wherein, δ is the distance on the optical axis between the lens component and the concave-convex lens component included in the fourth lens group, and D is the distance on the optical axis from the specimen surface to the lens surface of the fourth lens group closest to the image side.

5. The objective lens according to claim 1 or 2, characterized in that, The third lens group and the fourth lens group each contain a joint lens.

6. The objective lens according to claim 1 or 2, characterized in that, Spherical aberration is corrected by moving the second lens group to a position corresponding to the immersion liquid with a refractive index of 1.33 to 1.

40.

7. The objective lens according to claim 1 or 2, characterized in that, The fourth lens group has negative refractive power.

8. The objective lens according to claim 1 or 2, characterized in that, The first lens group includes three joint lenses.

9. The objective lens according to claim 1 or 2, characterized in that, The second lens group consists of two joined lenses.

10. The objective lens according to claim 1 or 2, characterized in that, The third lens group consists of a single lens component.

11. The objective lens according to claim 6, characterized in that, The following conditional expressions are satisfied. D / f≤7···(2) D / (NA 2 ·WD)≤35···(3) Where D is the distance on the optical axis from the specimen surface to the lens surface closest to the image side of the fourth lens group, f is the focal length of the objective lens, NA is the numerical aperture of the objective lens on the object side, and WD is the working distance of the objective lens.

Images